----- Original Message -----
From: "Poul Nissen" <[email protected]>
To: <[email protected]>
Sent: Monday, October 04, 2010 2:21 PM
Subject: Re: [ccp4bb] Radiation damage with crystals containing metal
centers (TaBr people chime in?)
[1] the signal from Ta6Br12 is enormous and one will typically focus on low
resolution (below 7 Å) so radiation sensitivity can be handled by a fairly
low dose data collection
We collected several data sets with Ta6Br12(2+) on the Na+,K+-ATPase (Morth
JP et al. 2007) and found that although we got the strongest anom. diff.
Fourier peaks from a data set collected on the Ta peak, we got far better
SAD phases from a data set collected on the high-energy remote wavelength.
This I think is also often observed for SeMet.
Interesting phenomenon--has it been documented, I wonder? I wonder which
datasets were collected first? If the peak was collected first, as usual I
think, and one assumes an exponential decay of the resonant signal as a
function of radiation dose, it makes sense that the resonant signal would be
more constant after the first data set, where the decay curve would have
flattened out a bit. This would also be true for two consecutive data sets
collected at high energy. Also, I think the decay function itself is steeper
at the peak wavelength, leading to a less-internally-consistent data set at
the peak. Does this argument hold water?
Jacob Keller
